It is previously known to manufacture covering material in the form of long webs, which are delivered in the form of rolls in order to be laid out on floors or in order to be put up as wall covering. The covering material referred to here consists of a plastic layer, which may extend through the whole thickness of the material or, as is often the case, which is carried by a substrate such as fibre web of glass fibre or of other fibre. In the most common commercial products, the plastic layer consists of polyvinyl chloride, PVC. One reason why this material has been selected to such a great extent is that it can be treated during manufacture with methods which in many respects are rational. Accordingly, PVC in the form of a plastisol may be applied onto a substrate with the help of a doctor blade by means of which a layer of the plastisol, with an adapted thickness, is applied onto the substrate passing the doctor blade. As suggested, the substrate may be included in the product or constitute a part of the manufacturing equipment and thereby not be integrated into the product. After the application, the plastisol may be gelled to such a solid form that the surface may be pattern printed or be subjected to other finishing treatment in order to achieve decorative effects. Finally, the PVC-layer is cured by means of heating. If a material in foam form is thereby desired, this may be achieved by means of using the plastisol with an addition of blowing agent. Thereby, it is also possible to provide the surface with a relief. Accordingly, it is possible to manufacture materials within a wide spectre with different character and appearance by means of this relatively simple manufacturing method
Despite the fact that PVC has very good processing properties and also properties in use, attempts have been made during recent years to replace this material with other plastic materials. The motive for this are environmental reasons. During combustion PVC forms, inter alia, corrosive hydrogen chloride.
When attempting to replace PVC in products such as, typically, surfacing materials, which are manufactured in long webs, manufacturing methods have been sought, which are not particularly aimed at the use of plastisol but which allow a wider range when choosing the material. Thereby, it has been an objective to make it possible to use so-called olefines as a manufacturing material. Amongst such material groups polyethylene and polypropylene may be mentioned. Due to its flexibility the material in products manufactured from these plastic types does not have to be mixed with plasticizers, and in the final destruction primarily water and carbon dioxide are formed during combustion, which give a low environmental impact.
These materials, however, are not transformable to a paste in the same way as PVC, which can be used for coating a base layer in the previously described way. Where the materials which are desirable for replacing PVC are concerned, one is obliged to resort to thermic manufacturing processes such as extrusion and calendering, which require large investments in machinery. In order to find a more advantageous alternative, it is suggested in U.S. Pat. No. 5,407,617 (Oppermann et al) to apply the plastic material in the form of particles onto a passing substrate by means of scattering. In this context, this forms means that the particles are fed out from a depository intended therefor by means of an actuator to enable them to fall freely from the actuator and down onto the substrate. Thereby, the particles form a layer on the substrate, the thickness of which may be adjusted by means of the transportation speed of the substrate and the feeding capacity of the scattering device. In the subsequent steps, the layer is stabilized by means of the particles being sintered together during moderate heating. In a further step, the layer is thereafter given its solid shape by means of cylinders heated to a higher temperature. According to the publication, decorative effects may be achieved by means of processing such as printing, relief formation or in another way.
The method of scattering a powder offers great possibilities to choose from different polymer types. However, the method causes considerable difficulties when it comes to achieving a reliable result. A number of different factors may disturb the deposition of the particles on the substrate, so that an uneven layer thickness is obtained, and it is particularly difficult to obtain the same layer thickness across the entire width of the web without obtaining thinning or bulging at the edges of the web. The difficulties become even greater if there is a desire to achieve decorative effects by means of a mixture of particles, particularly if these have different size and shape. Therefore, the method results in severe limitations to the choice of pattern.